Air heater and method of operating same



Nov. 15, 1921 1,649,605

' B. LJUNGSTROM ET AL AIR HEATER AND METHOD OF OPERATING SAME Original Filed May 2, 1927 2 Sheets-Sheet l Nov. 15, 1927.

1,649,605 B. LJUNGSTROM ET AL AIR HEATER AND METHOD OF OPERATING SAME Original Filed May 2, 1927 2 Sheets-Sheet 2 Mae Nov. 15,1921. 1,649,605

UNITED STATES mi'rau'r OFFICE.

nmenn munesrnoia AND BERTIL ALFRED munes'rnom, or srocxrronm, ewnnmr; SAID IBERTIL ALFRED mmvesrnom ASSIGNOR T SAID BIRGER munesrnom.

AIR HEATER AND METHOD OF OPERATING SAME.

Application filed May 2; 1927, Serial No. 188,349, and in Great Britain April 12, 1926. Renewed October 11, i

The present invention relates to air-heatproper. Such auxiliary air-heater may ers and to an improved methodpf operation either be built of corrosion resisting material advantageously used in connection wlth a1ror may be provided with easily replaceable heaters utilizing waste or smoke gases from walls or passed by the hotsmoke gases prior 55 5 furnaces as heating medium. to entering the air-heater proper in which In air-heaters, especially of the countercase the resulting high temperature of the current recupeiative type, corrosive matters auxiliary air-heater prevents condensation condense out of the smoke gases onto the of and corrosion by corrosive matters.

- surface of the heat conducting walls, with A second method of heating embodies the 60 the result that the walls arecorroded right by-passing of hot gases to be mixed with through in a comparatively short time and the air before heating in the air-heater smoke gases and air mix through the openproper, such by-passing starting either from ings produced by said corrosion, thus .ren the hot air exhaust or the smoke gas supply dering the air-heater unfit for-further use. of the air-heater proper. A fan arrange- 65 The corrosion appears chiefly in the colder ment coupled to the by-pass for the heatin" part of the air-heater and is caused by the gases may be provided, if necessary. low temperature of the entering air cooling If, however, the by-pass is led from the the walls of the air-heater well below the hot air side to the suction side of the fan temperature at which the corrosivematters producing the air pressure necessary for the 70 contained in the smoke gases condense. air-heater proper an extra fan in the by The present invention has for its object pass will in most cases be unnecessar to remove the above explained difficulties. In many cases only fifteen to twenty per To this end, the present invention provides cent of the total volume of the hot gases a method of operating air-heaters of the type need be carried by the by-pass. 7

in which air, before passing into a furnace The hot gases ought to be well mixed with or the like, is heated by means of the smoke the air to be heated, for which purpose spegases from the furnace or the like, which cial arrangements are embodied in the inconsists in mixing the air to be heated, with vention.

hot air or smokegases taken from a suit- In order more clearly to understand the 30 able hot air supply or a suitable smoke gas invention, reference is made to the accomsupply located in front of the smoke gas expanying drawings whichillustrate by way haust of the air-heater, counted in the diof example some embodiments of arrangerection of movement of said gases, in order ments according to the invention.

to maintain all parts of the heat-transmit- In said drawings ting walls of the air-heater at a temperature Fig. 1 is a side view of anair-heater above that at which condensation of corroprovided with a by-pass from the smoke sive matters from the smoke gases takes gas supply to the air inlet, the by-pass beplace. By this means corrosion of the heat 111g fitted with a fan. transmitting walls of the air-heater is pre- Fig. 2 is a side elevation of an air-heater vented or at any rate keptwithin practicable showing a by-pass between the hot air outlimits. let and the suction side of a fan for the In most cases an increase of about 50 0. cold a1r. in the temperature of the air prior to bein F 1g. 3 IS a section parallel to the axis of heated inthe air-heater proper is found su the fan of Fig. 2 and of the end of the 45 -ficient to raise the temperature of the walls by-pass at the suction side of the fan.

of the airheater abov the boiling point of Flg. 4 is a cross section through the end water 0.) of the by-pass and the fan rotor.

The preliminary heating of the air to be Fig. 5 is a cross sectlon parallel to the mixed with the cold air supply may be efaxis of the fan fitted with another arrange- 100 50 fected by an auxiliary air-heater either sepment for the inlet of the hot gases from Mate rom or integral with the air-heater the by-pass.

Fig. 6 shows a cross section of the fan rotor and inlet tubes for the same arrangement.

-Fig. 7 is a section through-the axis of a fan showin the heating gases introduced into the di user of the fan.

In Fig. 8 is shown a longitudinal section of the air inlet pipe to the air-heater together with an arrangement for introduc- I ing air through the fan 14.

the by-pass 12 starting Fig. 2 shows the air passage 11 of the air-heater 10 fitted with a fan 15 supplying air to the air-heater and receiving at the centre of its suction side the hot air from from the hot air outlet 16 of the air-heater, the smoke gas inlet being designated by 13 and the outlet therefor by 25. a

Fig. 3 shows the same fan 15 in longitudinal section withthe end 18 of the byass pipe 12 situated inside the fan rotor 1 As shown in Fig. 4, the end 18 is provided around its peripherfi with longitudinal openings adapted to ring the issuin hot air in rotation inside the fan rotor 1 resulting in the thorough mixing of the hot and cold air. y p In Fig. .5 an arrangement for the same urpose is shown in longitudinal section.

11 this case the by-pass 12 is connected to an annular chamber 19 located around the suction inlet of the fan; From this chamber, tubes 20 are axially and symmetrically disposed at the inside of the circumference of the fan rotor 17 Fig. 6 shows the tubes 20 and rotor 17 in cross section. The tubes 20 are slotted along their outer edges so as to cause the hot air to issue in a more or less tangential direction.

Fig. 7 illustrates the fan 15 fitted with a bent part of the by-pass 12 arranged around the difiuser of the fan 15, tubular tangential connections 23 being rovided between the pipe and the interior of the diffuser.

Fig. 8 is a longitudinal section through the air passage 11 of the preheater. This passage 11 is fitted with an outside annular chamber 21 receiving hot gases from the lay-pass 12 and conducting the same into the passage 11 with the aid of intermediate tangentlal nozzles 22 shown also in Fig. 9.

The hot gases are also in this case put into rotation for the purpose of effecting a thorough mixing with the inlet air.

In the foregoing we have described only a few means for carrying our invention into practical effect. It should, however, be well understood that the invention also in cludes other alternatives to the same effect as for example taking the heating gases directly from the boiler supply or from another auxiliary air-heater or similar measnres.

What we claim is 1. In a method for preventing condensation of corrosive matters in exhaust gases traversing an air preheater, the step of preheating the air rior to entrance in the preheater by a uid having a temperature higher than that of the exhaust gases leaving the preheater.

2. In a method for preventing condensa tion of corrosive matters in exhaust gases traversing an air preheater, the step of mixing the air prior to entrance in the preheater with a heated fluid of a temperature higher than the temperature of the exhaust gases leaving the preheater.

' 3. In an air preheater, a passage for air to be heated, a passage for hot gases to be cooled, means permitting heat exchange between the air and hot gases, and means for preventing condensation of cooled gases in said preheater comprising means for pre heat'ng the air by a heated fluid having a temperature higher than that of the exhaust gases leaving the preheater.

4. In an air preheater, a passage for air to be heated, a passage for hot gases to be cooled, means permitting heat exchange between the air and hot gases, and means to preheat the air before entrance into the preheater with gas having a temperature higher than that of the exhaust gas leaving the preheater.

5. In a method for preventing condensation of corrosive matters in exhaust gases traversing an air preheater, the step of mixing the air prior to entrance in the preheater with heated air having a higher temperature than the temperature of the exhaust gases leaving the preheater.

6. In an air preheater. a passage for air to be heated, a passage for hot gases to be cooled, means permitting heat exchange betwen the air and hot gases, means to preheat the air before entrance into the preheater comprising a by-pass for conducting a portion of the heated air from the air outlet of the preheater to the air inlet of the preheater.

7. In an air preheater a passage for air to be heated, a passage for hot gases to be cooled, means permitting heat exchange between the air and hot gases, and means to preheat the air beforeentrance into the preheater comprising a by-pass for conducting preheater and devices for intimately mixing the two fluids.

8. In an air preheater, a passage for air to be heated, a passage for hot gases to be cooled, means permitting heatexchange between the air and hot gases, and means to preheat the air before entrance into the preeater comprising a by-pass for conducting a portion of the heated air to the inlet of the air passage and devices for intimately mixing the two-fluids including nozzles for introducing said heated air into said other air.

9. In an air preheater, a passage for air to be heated, a passage for hot gases to be cooled, means permitting heat exchange between the air and hot gases, and means to preheat the air before entrance into the preheater comprising a by-pass for conducting a portion of the heated air to the inlet of the air passage and devices for'intimately mixing the tWo fluids including nozzles for introducing said heated air into said other air, said nozzles being arranged to impart rotary motion to said heated air after delivery from the nozzles.

10, In an air preheater, a passage for air to be heated, a passage for hot gases to be cooled, means permitting heat exchange between the air and hot gases, and means to preheat the air before entrance into the preeater comprising a by-pass for conducting a portion of the heated air to the inlet of the air passage and a fan in said by-pass.

In testimony whereof we aflix our signa- I tures.

BIRGER LJ UN GSTRfjM. BERTIL ALFRED LJ UN GSTROM. 

